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CSI # 16xxx – Digital Static Transfer Switch, Low Amperage

Digital Static Transfer Switch (DSTS)

SS3 Low Amperage, 2 Source, 3 Pole




These specifications describe requirements for a [200] [400] [600] [800] [1000] Amp Digital Static Transfer Switch (DSTS) at [208] [380] [415] [480] [600] VAC, 2 source, 3 phase, 4 wire (neutral not switched), 60 Hz.


This system shall consist of one complete DSTS and shall incorporate hockey puck-style Silicon Controlled Rectifiers (SCRs) as the switching elements and have a circuit breaker topology consisting of total of 6 non-automatic, plug-in circuit breakers - two (2) input, two (2) bypass and two (2) output. The short circuit withstand of the DSTS shall be 100kAIC for the 200 through 600 amp models and 65kAIC for the 800 and 1000 amp models.


The entire DSTS line-up shall be designed with maintenance access in mind allowing access for infrared scanning of critical power connections (power stage, breaker assemblies, breaker connections, heat sinks etc.) without the need to remove or disassemble any sub-assembly within the system. Power cable entrance and exit shall be from the bottom.


The manufacturer shall design and furnish all materials and equipment to be fully compatible with electrical, environmental, and space conditions at the site. It shall include all equipment to properly interface with and operate in conjunction with the AC power source, UPS system, and generator system.


The DSTS equipment and components shall be manufactured in compliance with the applicable requirements of the following standards:

  • ANSI/NFPA 70 (2008)

  • National Electrical Code (2008)

  • NEMA (All applicable standards)

  • Underwriters Laboratories (UL). The DSTS shall be ETL Listed to UL 1008. Submit documentation with the bid indicating listing agency and file number.

  • ANSI/IEEE C 62.41 Surge/Noise suppression


The following definitions shall apply throughout this specification:

  • DSTS - a complete automatic digital static transfer switch and associated accessories.

  • Bypass - direct power flow from one source to the critical load as required for maintenance of the DSTS without disruption of the load.

  • Redundant - inclusion of one more device than is required to achieve continuous operation without disruption of the load.

  • Owner, User or Buyer - owner (or its designated representatives).

  • Manufacturer - the firm or corporation who will manufacture and deliver the DSTS equipment specified herein.

  • Specifications - technical instructions described or portions of standards referenced herein, and any addenda thereto.


1.4.1Environmental Requirements

The DSTS shall be capable of withstanding any combinations of the following environmental conditions without mechanical or electrical damage or degradation of operation.

      • Operating ambient temperature: 0 to 40°C.

      • Non-operating storage temperature: 0 to 80°C.

      • Relative humidity: 0 to 95% non-condensing.

      • Noise Level: <65dba at six feet from the DSTS.

      • Maximum operating altitude without de-rating: 6000 feet above sea level.

      • Equipment shall be designated for indoor use in a clean (dust-free) temperature and humidity controlled environment.

      • AC to AC efficiency defined as the ratio (expressed as a percentage) of AC output kW to AC input kW at full nominal rating at 0.8 power factor load shall not be less than 99%. Provide proposed efficiency data in specification compliance form in the proposal, if other than this figure.

1.4.2Electrical Characteristics

      • Nominal Source Voltages: [208] [380] [400] [415] [480] [600] volts AC plus ± 10%, 3 phase, 3 or 4 wire + ground (neutral not switched).

      • Source Frequencies: [60Hz] [50Hz] ± 5%.

      • Continuous Current Rating: [200] [400] [600] [800] [1000] Amps.

      • Load Power Factor: Unity to .50 lagging or leading.

      • Overload Rating:

  • 125% for 30 minutes

  • 150% for 1 minute

  • 200% for 10 seconds

  • 1000% for 3 cycles

  • 1500% for 1 cycle

      • Harmonic Current fed back from the load: Unlimited

      • Source Voltage THD in the line feeding the load:

  • Maximum 5% total harmonics or as acceptable to the load.

  • Maximum 3% single harmonic or as acceptable to the load.

      • Voltage Transient Withstand without failure or mis-operation, present on the line: Up to 20,000-volt spike, per IEEE C62.41 Category C3 Standards. Such transient levels shall not effect the operation of the DSTS except to cause a transfer due to over-voltage beyond pre-set limits.

      • Over-current Protection: The non-automatic internal breakers shall be rated at a continuous [200] [400] [600] [800] [1000] AF/NA current rating (frame rating should be higher if the breaker is de-rated 80%), with magnetic trips set at their highest setting to allow coordination with up-stream protective devices.

      • Short circuit and overload rating shall be such that the unit does not drop the load while such conditions are being protected or acted on by properly rated thermal-magnetic circuit breakers in the owner’s distribution system.

1.4.3Construction, Enclosure and Access

The DSTS assembly shall be constructed in modular configuration for maximum ease of maintenance, installed in NEMA Type-1 metal enclosures made of 11 gauge steel frame and 16 gauge steel sides, with provisions for computer room installation (with casters and leveling feet). Sheet metal parts shall be either electroplated or primed and painted. Color shall be manufacturer’s standard.

      • Individual enclosures shall require front access for equipment operation and removal of serviceable parts such as pc boards, SCR assemblies and plug-in breakers. Front doors shall be lockable to provide access only by authorized personal. Deadfronts shall be provided behind the lockable front doors to allow safe operation of breakers and to cover all energized parts.

      • Individual enclosures shall also require rear access or one side access for installing, torquing or IR scanning of customer connections. Left or right side access, dictated by operational position, must be specified at the time of order. Side and rear access doors shall be lockable.

      • All circuit breakers shall be plug-in or rack-out/draw-out.

      • The enclosure shall have all normal operating controls, instrumentation, display and lights mounted on the front door. All control setting adjustments for voltage level sensing shall be via a menu driven software on a color LCD panel on the front of the unit. Adjustments options of the menu shall require the knowledge of a security access code so as to not allow unauthorized staff to make such adjustments. The door-mounted controls shall be for human interaction with the DSTS’ internal logic only. In the absence of or malfunction of the door-mounted controls (e.g. if they are disconnected or not operational) the DSTS shall enable an internal set of PCB-mounted auxiliary operators that allow basic control functions to be effected from inside the DSTS by qualified service personnel.

1.4.4Modularity of Construction

Sub-assemblies shall be constructed for ease of access and replacement of parts. Circuit boards shall use industry-accepted connectors. Connectors shall be chosen such that erroneous connections are not possible. SCR assemblies shall be pullout style for ease of replacement and minimal down time.

1.4.5Bracketing and Wiring

Brackets and securing hardware shall be electroplated with corrosion resistant material. Internal wiring conductors shall be combined into cables or bundles and tied securely together. All wiring shall be clearly marked. All logic and control connections shall be routed away from any power runs for noise suppression.

1.4.6Conducting Material

All internal bus work shall be fabricated of custom-formed copper. All bus work shall be rated for 1000 amperes per square inch cross section or to not exceed a temperature rise of 50 degrees Centigrade in free air. Aluminum is not acceptable for the referenced requirements. If the owner or their representatives discover noncompliance in this area during or after completion of installation (regardless of signed acceptance tests), the DSTS manufacturer is responsible for replacing all areas of such noncompliance at its own expense including materials, freight, and site labor expenses.

1.4.7Material and Workmanship

All materials and parts comprising the DSTS shall be new, of current manufacture, high grade, and free from all defects or imperfections, and shall not have been in prior service, except as required during factory testing. Workmanship shall be of the highest quality.

1.4.8Short Circuit Bracing

      • Unit construction and component selections shall incorporate ratings, support, and bracing methods to allow for the specified short circuit withstand rating of the unit (including all electro-mechanical and power electronic devices, interconnections, cable and bus work).

1.4.9EMI Susceptability

Radiated and conducted EMI generated within the units shall be suppressed to prevent excessive interference with associated nearby electronic equipment. Units shall also not be susceptible to mis-operation due to EMI or RFI generated by a hand held VHF or UHF transceiver from a distance of 24 inches in front of a unit, with the doors closed.

1.4.10Surge/Noise Suppression

Power SCRs used in the system shall be conservatively rated for dv/dt of at least 800v/u-Sec. The design of the unit and component selections shall provide capability to withstand noise spikes per ANSI/IEEE C 62.41 standards (2kv impulse) without malfunction or any device breakdowns or sporadic transfers. All power supplies shall incorporate noise immunity circuits.
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